1. Field of the Invention
The present invention relates to an imaging device for simultaneously picking up images in plural visual field directions by a single image pickup element, and a vehicle circumference visualizing apparatus using the imaging device.
2. Description of the Related Art
Conventionally, a device for simultaneously picking up images by an single image pickup element in three visual field directions on both forward left and forward right sides, and the forward slanting lower side of the imaging device is known (See JP-A-2000-089301). FIGS. 11 and 12 respectively show a schematic sectional side view (XI-XI sectional view of FIG. 12) and a schematic sectional plan view of the conventional imaging device.
In the conventional imaging device 100, an image pickup lens 129 is arranged in front of a single image pickup element 131. A prism 156 of a triangle pole shape is arranged in the upper side area (shown by a symbol “Vu” in FIG. 11) of a vertical view angle (shown by a symbol “V” in FIG. 11) of the image pickup lens 129 on a front side of the image pickup lens 129. Lights from the visual field directions on both the forward left and right sides (shown by symbols “143L” and “143R”, respectively in FIG. 12) of the imaging device 100 are reflected on the image pickup lens 129 side by the prism 156, and pass through the upper side area Vu of the vertical view angle V of the image pickup lens 129, and are incident to the image pickup lens 129. These lights 143L, 143R are then formed as images in the image pickup element 131 through the image pickup lens 129. Light from the visual field direction on the forward slanting lower side of the imaging device 100 (shown by a symbol “143F” in FIG. 11) passes through the lower side area (shown by a symbol “Vd” in FIG. 11) of the vertical view angle V of the image pickup lens 129 and is directly incident to the image pickup lens 129, and is formed as an image in the image pickup element 131 through the image pickup lens 129. Thus, the images are simultaneously picked up by the single image pickup element 131 in the three visual field directions on both the forward left and right sides and the forward slanting lower side of the imaging device 100.
When the imaging device 100 of the kind is used in a vehicle circumference visualizing apparatus, the imaging device 100 is arranged in the vehicle front portion and picks up images of dead areas (blind corners) in the three directions constructed by both the forward left and right side directions and the forward slanting lower side direction of the vehicle. In a case above, it is desirable to pick up the image in the forward slanting lower side direction of the vehicle (i.e., the visual field direction on the forward slanting lower side of the imaging device 100) at a wide angle so as to display the image in a wide range from a forward just near position to a distant position of the vehicle.
Therefore, an idea has been proposed for picking up the image in the visual field direction on the forward slanting lower side of the imaging device 100 at a wide angle by setting the entire view angle of the image pickup lens 129 to a wide angle by using a wide angle lens as the image pickup lens 129.
However, in the above proposal, the pickup images are set to wide angles for the upper side area Vu (i.e., the visual field ranges in the visual field directions on both the forward left and right sides of the imaging device 100) as well as the lower side area Vd of the vertical view angle V of the image pickup lens 129 (i.e., the visual field range in the visual field direction on the forward slanting lower side of the imaging device 100). Therefore, the images are picked up at wide angles for the pickup images in the visual field directions (i.e., both the forward left and right side directions of the vehicle) on both the forward left and right sides of the imaging device 100 as well as the pickup image in the visual field direction on the forward slanting lower side of the imaging device 100. Therefore, the above proposal has disadvantages in that an approaching object displayed in the pickup images in both the forward left and right side directions of the vehicle is displayed as a small object.